1. Field of the Invention
The invention is directed to a diode laser arrangement with a plurality of diode laser arrays, each of which is connected with a thermal contact surface of a heat-spreading carrier and contains a p-n junction plane parallel to the thermal contact surface. The carriers are fastened adjacent to one another in the array direction to a cooling surface of a common cooling element so as to be electrically insulated, so that the cooling surface extends parallel to the thermal contact surfaces.
2. Description of the Related Art
High-power laser diodes which are generally constructed as arrays and are stacked to form two-dimensionally emitting surfaces with increased radiating power are used for industrial laser machining of material, for pumping solid state lasers and in the field of medical engineering. Improved radiation characteristics can be achieved by collimating the so-called fast axis (perpendicular to the p-n junction plane) and also, additionally, by collimating the slow axis. Finally, beam shaping or beam symmetrization leads to a further improvement in beam density and beam quality. Typical dimensions are about 5 to 12 mm for the array width and 5 to 100 mm for the stack height. Up to 50 laser diode arrays can be arranged one on top of the other in a laser diode stack.
Stackable systems require efficient cooling due to their compact construction, especially since the distance between the arrays is to be kept as small as possible in order to achieve higher power densities. In the past, this led to the development of water-cooled heatsinks containing microchannels in order to achieve a lower thermal resistance with extremely compact dimensions.
Microchannel heatsinks of the type mentioned above are known, for example, from DE 43 15 580 and DE 197 50 879. U.S. Pat. No. 5,105,429 and U.S. Pat. No. 5,105,430 use these heatsinks expressly for the purpose of generating stackable systems in which the coolant is guided through the stack in continuous paths. Each of the microchannel heatsinks in the stack comprises a multilayer structure with microchannels in the upper layer and has inlets and outlets connected to the continuous paths.
U.S. Pat. No. 5,105,429 and U.S. Pat. No. 5,105,430 are also referenced in DE 43 35 512. The latter uses a so-called heatspreader to substantially increase the small heat-conducting surface of the laser diode and, therefore, to achieve a multiple increase in cooling efficiency.
It is also known to connect a laser bar with a substrate which is divided into partial regions and which rests on a heatsink. In EP 0 590 232 A1, in order to prevent thermal crosstalk between the individual laser diodes of the laser bar, areas with poor heat conductivity are arranged below a region between the individual diodes; in DE 198 21 544 A1, the laser diodes of the laser bar communicate with an individual web of dielectric material.
DE 195 36 463 A1 describes a laser diode component with a semiconductor body which is fastened to a heatsink. The heatsink comprises a cooling body with an electrically and thermally conducting connection plate to which the semiconductor body is fastened. A large number of these laser diode components can be fabricated as a unit and subsequently divided up.
In the modular construction according to DE 43 15 580 which is suited in principle for stacking, the functions of a microchannel heatsink are divided between five layers. In a microchannel plate or distributor plate, the coolant supplied via an inlet is distributed to the microchannels located below a diode laser fastened to the cover layer. The coolant is conducted, via connection channels in an intermediate layer, into a collecting plate which connects to an exit. A bottom plate closes the microchannel heatsink at the bottom.
Although the direct (active) liquid cooling is extremely effective, the microchannel heatsinks also have drawbacks. For instance, the structures of the microchannels are complicated to produce. The coolant, frequently water, places very high demands on the liquid-conducting materials, seals and coolant quality due to the close proximity to the sensitive semiconductor components.
Problems also arise because the liquid-guiding channels must traverse areas with different electric potentials. If elaborate steps are not taken, very high electrical fields sometimes occur which can trigger highly complex electrochemical processes.
Enclosing the stacks for protection against external environmental influences necessitates particularly great efforts for eliminating or preventing the formation of condensation in the housing due to residual leak rate.
There are also disadvantages connected with the stacking itself. As the distance between the arrays is reduced, not only is an increasingly effective cooling required, but the reduction itself is additionally bound by geometric limits.
An arrangement suggested in DE 43 15 580, in which a plurality of laser diode bars are mounted on a large-area microchannel heatsink, is also not capable of closing the geometry-dependent free space between the radiating surfaces of edge emitters.
Finally, the diode stacks have the added disadvantage that they are limited only to determined applications because of the predetermined configuration of their radiation field.